1. Field of the Invention
The present invention relates to a sewing machine having a presser foot which reciprocates in relation with the reciprocative motion of a sewing needle.
2. Related Art Statement
There is known a sewing machine, such as an embroidery sewing machine, which includes a work-fabric presser foot which vertically reciprocates in relation with the vertical reciprocative motion of a sewing needle. FIG. 8 shows an example of such sewing machines, in which a needle bar 101 is supported by a first and a second bearing 102a, 102b of the sewing machine, such that the needle bar 101 is vertically movable. The needle bar 101 includes, at a lower end portion thereof, a needle holder 101a to which a sewing needle 103 is secured. The needle bar 101 vertically reciprocates when receiving the drive force (i.e., rotary motion) of an electric motor via a drive shaft and a crank mechanism (not shown).
A fabric presser foot 104 fits on a lower portion of the needle bar 101. The presser foot 104 is formed by bending an elongate plate, and includes a lower-end bent portion serving as a fabric presser toe 104a. The presser toe 104a has a through hole (not shown) through which the sewing needle 103 passes. The presser foot 104 further includes an upper-end bent portion 104b, and a relief spring 105 is disposed between the upper-end bent portion 104b and a needle bar connecting stud 101b fixed to the needle bar 101. The presser foot 104 is biased downward by the relief spring 105, so that normally an intermediate bent portion 104c (more specifically, bearing member therefor) of the presser foot 104 is held in abutment contact with the needle holder 101a of the needle bar 101.
When the needle bar 101 starts to move downward from the position shown in FIG. 8, the presser foot 104 moves downward together with the needle bar 101. Subsequently, the upper-end bent portion 104b of the presser foot 104 comes to engage an abutment 102c of the second bearing 102b, so that the downward movement of the presser foot 104 is stopped. Thus, the presser toe 104a of the presser foot 104 is held slightly above a work fabric into which an embroidery is formed by the sewing machine. Then, only the needle bar 101 (and the sewing needle 103) continues to move downward to the lower dead position thereof, so that the sewing needle 103 penetrates the work fabric to form a stitch.
When the sewing needle 103 moves upward from the lower dead position thereof, the presser foot 104 continues to be held slightly above the work fabric until the needle holder 101a of the needle bar 101 comes to engage the intermediate bent portion 104c of the presser foot 104. Consequently the presser toe 104a of the presser foot 104 effectively prevents the work fabric from being dragged up by the sewing needle 103 when the sewing needle 103 moves upward after a needle thread carried thereby has been locked with a shuttle thread at the lower dead position of the sewing needle 103. After the needle holder 101a has engaged the intermediate bent portion 104c of the presser foot 104, the needle bar 101 and the presser foot 104 move upward as a unit.
However, in the above-described conventional presser-foot arrangement, the relief spring 105 is necessarily disposed between the upper-end bent portion 104b of the presser foot 104 and the connecting stud 101b of the needle bar 101. The provision of the relief spring 105 at that position results in increasing the vertical dimension of the needle bar 101, thereby increasing the vertical dimension of the free-end or head portion of the horizontal arm of the sewing machine where the needle bar 101 is disposed. This eventually leads to increasing the overall size of the sewing machine. Additionally, each time the sewing needle 103 moves downward, the upper-end bent portion 104b of the presser foot 104 collides with the abutment 102c of the second bearing 102b, for stopping the downward movement of the presser foot 104 slightly above the work fabric. Thus, impact noise is generated due to the collision of the two members 104b and 102c.
A second example of the above-described sewing machines is disclosed in Non-Examined Japanese Patent Application laid open under Publication No. 61(1986)-159983. The disclosed sewing machine includes a presser-foot bar which supports a presser foot and is directly connected to a crank rod connecting between a needle-bar crank and a needle bar (or a sewing needle). However, since the presser-foot bar of the prior sewing machine is directly connected to the needle-bar crank rod, the presser-foot bar substantially follows the vertical displacement of the needle bar or sewing needle. Thus, it is very difficult to make the stroke of the presser-foot bar smaller than that of the needle bar and thereby reduce the rate of change of the vertical displacement of the presser-foot bar. Therefore, it is very difficult to cause the presser foot to move as if it were stopped slightly above a work fabric to hold down the fabric, for a longer duration of time than the duration of time in which the needle bar is controlled to move as if it were stopped around the lower dead position thereof. Additionally, it is difficult to make the phase of the presser-foot bar largely different from that of the needle bar.
A third example of the related sewing machines is disclosed in Non-Examined Japanese Patent Application laid open under Publication No. 63(1988)-296783. The disclosed sewing machine includes a presser foot bar which supports a presser foot, and an exclusive crank mechanism and a very complex link mechanism which cooperate with each other to transmit the drive force of a drive shaft to the presser foot. With this presser-foot arrangement, an increased number of parts are needed for reciprocating the presser foot, therefore the production cost of the sewing machine is increased.